Add missing GHL instruments

[TheBoxyBear]

As specified in the format spec, GHL now supports Rhythm and Coop like with Standard instruments.

• [x] Add entries to InstrumentIdentity and GHLInstrumentIdentity
• [x] #90
• [x] Add headers to ChartFormatting
• [x] Honor components in ChartFileReader
• [x] Add members to InstrumentDifficultySet
• [x] Add heard to IniFormatting
• [x] Honor difficulty members for Metadata